The method and apparatus of U.S. Pat. No. 4,151,389 teaches welding operations at a current of the order of 2600 A. A current of this magnitude generates strong magnetic fields, so that special measures are required to permit the introduction of a metal powder into a welding gap during the welding operations. The metal powder serves as a filler material, and any surplus powder is allowed to fall by gravity into a slag bath. It is desirable that no current pass through the metal powder.
An inert carrier gas conveys the metal powder through flexible tubes outside the welding gap, and ejects it towards the front or rear wire electrode pair closely above the surface of the slag of the pool. Conventional transport by gravitational force, as has been used hitherto, no longer suffices for this purpose. Thus, there are provided powder supply or conveyer devices, which operate by means of a neutral supply gas. Additionally, any associated tube conduits must be spaced at a predetermined distance from the electrodes, and furthermore only the discharge openings of the supply nozzles may be positioned near the surface of the slag bath. The nozzles are mounted on, but insulated from, the current-carrying conduits for the electrodes, and their spacing and direction are adjustable by means of supports.
In order to ensure a welding process free of any disturbances, the supply nozzles for the metal powder must be directed precisely towards the center of the pairs of wire electrodes, and must terminate just above the surface of the slag bath. Otherwise short circuit paths of metal powder may form between any metal sheet edge, and the wire electrodes. This requirement for precision of the metal powder supply is met only through the most careful adjustment of the nozzles. Furthermore, this embodiment of a metal powder supply is restricted to two pairs of wire electrodes.
An earlier report dealing with "A substantial increase of the welding velocity during electroslag welding while simultaneously improving the quality of the weld", published in "DVS Berichte, Vol. 31," provides inter alia details of the composition of the metal powders used.
An early Russian publication "On the Effectiveness of Using Filler Metal in Powder Form in Electroslag Welding" Svar. Proiz, 1969, No. 11, pp. 18-19, shows that the use of metal in powder form as a filler increases the productivity of electroslag welding, and greatly improves the properties of the welded joint. A later Russian publication "Electroslag Welding with Powdered Filler Metal," Svar. Proiz, 1972, No. 5, pp 17-19, relates to a method and equipment which have been developed for electroslag welding of 25-60 mm mild and low-alloy steels using filler metal and solid section electrode wire.